Response properties of cortical neurons are influenced by the inputs they have received in the recent past. Knowledge of precisely how recent stimulus history, and ultimately, experience alters the brain is central to understanding normal sensory coding as well as principles of brain reorganization following injuries. The goal of this research proposal is to understand the neural computations that underlie an important and pervasive form of this history-dependence, sensory adaptation, using the visual system as a model. Previous work has established that adaptation alters neuronal response properties of cortical neurons as sensory signals cascade through the hierarchical stages of visual processing. However, the precise modifications induced by recent stimulus history across cell categories (excitatory vs. inhibitory), timescales of exposure, and stages of cortical processing has been relatively unexplored. Filling these gaps in the current knowledge will provide an enhanced understanding of how adaptation modulates signal processing and functional reorganization of visual cortical networks. To achieve these goals, we will perform multi-tetrode recordings in the visual cortical areas V1 and V2 in anesthetized macaques, and sample many neurons simultaneously across the laminar stages in the two cortical areas. In Aim 1, we determine the effects of short-term and long-term adaptation in two functionally distinct cell categories, excitatory neurons and inhibitory interneurons, distinguished on the basis of the shape of recorded spike waveforms. In the two cell categories, we will determine the alterations in selectivity and neural response properties induced by adaptation to preferred and non-preferred stimuli. The results of this study will be important for understanding how the structurally and functionally distinct components of the cortex integrate recent stimulus history along with new information at the neuronal and network level to provide a unified and stable percept of the visual scene. In Aim 2, we determine how adaptation in an early visual cortical processing area (V1) is related to adaptive effects in a downstream and reciprocally connected cortical area (V2). Specifically, we will determine whether adaptation occurs primarily in one area and its effects then propagate, or, alternatively, whether adaptation arises independently in each area. The findings from this study will provide an enhanced understanding of how computations carried out across feedforward and feedback connections both within and across cortical areas are influenced by recent stimulus history.